Apparatus for roasting ores



Jan. 2, 1923.

C. G. FINK.

APPARATUS Fox RoAsnNG oms.y

FILED FEB.18.1921.

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- useful Improvements in Apparatus Roasting Ores; and I do hereby declare the Patented Jan; 2, 1923'.

UNITED ysra'nasA COLIN G. INK, 0F YONKEBS, NEW YORK, ASSIGNOR TOVGUGGENHEIH BROTHERS; 01E'Y PATENT orales.

NEW YORK, Y., A COPARTNERSHIP. l

APPARATUS FOR i ROASTING OBES.

To all rw/Lom t may concern:

Be it known that I, COLIN G. FINK, a citizen 'of the United States, residin at Yonkers, in the county of Westchester, tate of New York, have invented certain new afnd or following to be a full, clear, and exact description of the/invention, such as will enable others skilled in the art to which it appertains to make and use the same.

This inventionA relates to apparatus for roasting ores and has-for its object the provision of certain improvements in such apparatus.

Many different types of furnaces are in common use vtoday for roasting ores. To some extent, the type of furnace employed is determined by the nature of the ore to be roasted. Thus, in roasting blend (sulfide of zinc), it is common practice to employ furnaces of the Well known Matthiessen and Hegeler type. Blend -is also commonly roasted in furnaces of the'wcll known Herreshofl' type, which type of furnace is likewise frequently employed in roasting copper and tin ores. Speaking generally, ore roasting apparatus may conveniently be divided into three general types of classes, (l) reverberatory furnaces, (2) muile furnaces, (3) kilns. All of these furnaces have a hearth or bed for holding the ore during the roasting operation and appropriate instrumentalities are usually rovided for working or rabbling the ore uring roasting, and, in most furnaces, for progressively moving the ore along the hearth or bed of the furnace.

At the present time, it is the usual practice to construct the hearth or bed of roasting furnaces of refractoryl material, such as magnesite, silica, alumina, etc. Such refractory materials have poor heat conductivity and, where the heat for roasting must be transferred through a refractory wall or conveyed by conduction through such a wall, the heating efficiency is relatively low. Thus, in muflle furnaces where the heat for roastingis, to some extent at least, conveyed to the charge' through the walls of the vmuiiie,

the poor heat conductivity of the refractorymaterial of which the muie is customarily made results in a low heat efficiency.- Simi-i` lai-ly, in roasting furnaces of the multiplestage type, the poor heat conductivity of the superposed hearths and walls of the furnace f (when made of refractory material) prevents an satisfactory transfer and distribution of eat through the furnace by-heat conduction. Even in the roasting of ores (more lparticularly sulphide ores) which require no external heat, it is highly desirable to transfer heat from the inherently hotter to the inherently cooler parts of the furnace. Where such parts of the furnace as might effect such a transfer of heat by conduction are made of refractory material, the poor heat conductivity of the refractory matcrial presents a formidable obstacle to the at tainment of the desired result.

The present invention contemplates the provision of an improved ore roasting apparatus 1n which such furnace walls as are exposed to the'roasting temperatures and which contribute by conduction'to the distribution of heat through the furnace are made of an alloy composed chieiiy of iron and chromium. Thus, the invention involves the provision of an ore roasting yfur-- nace having a hearth or bed made of an alloy composed chieliy of iron and chromium.

The iron-chromium alloy is a metallic material possessing excellent heat conductivity, and by the practice of the invention greatly increased heat economy and heat efliciency are attained, as comparedv with furnaces in which the corresponding parts are constructed of refractory material.

In the accompanying drawing, I have illus; trated merely for purposes of explanation a multiple stage roasting furnace of a well known. type. VThis furnace comprises a plu4 rality of superposed hearths 5 which, in accordance ,with the present invention are made of an alloy of iron and chromium. If

desired, the side walls 6 of the roasting chambers mayalso be lined with the alloy of iron and chromium,`but in order to prevent.

undue radiation of heat the main furnace structure 7 should bemade of lire brick or other appropriate heat-insulating material.'L

As a result ofv my researches and investigations, I have found thatl the alloy of iron and chromium in order to'. satisfacchromium.

vtol-ily the purposes ,ofthe y presentinvention I erosion or wearing awa-y ofv the alloy, sink,A-

ilar to that which takes place iflordinary iron were employed under similar condltlons. In most instances, I find that the` optimum results are secured when the iron-chromium alloy contains 'from about 33% toaboutv 36% of chromium. Hlgher percentages of chromium increase y the resistance ofl the alloy'to erosion, but at the same time such higher amounts of chromium render the alloy brittle and increase its cost, so that for most practical purposes, the iron-chromium alloy should not contain over about 36% of chromium. I have, however, secured satisfactory results for the purposes of the invention with alloys of iron and chromium containingV up to of In carrying out the invention, the furnace hearth, bed, wall, muflie or the like, is fabricated in any suitable manner of an iron-chromium alloy of the composition hereinbefore described. For example, the hearth, or the like, may be made by casting in sand molds, or may be made up of one 'or more appropriately shaped castings of an iron and chromium alloy.

In addition to iron and chromium, the alloy may, and usually will, contain carbon (one percent more or less), silicon (a fraction of one percent), and other innocuous impurities. An excessive` amount of carbon in the alloy should be avoided since when present in excess carbon reduces the mechanical strength of the alloy. The alloy may also contain, in small amount, other alloying metal or metals.

The alloy composed chieiy of iron and chromium may be made by various methods. I have found it entirely satisfactory to first melt, in a magnesite-lined crucible of an electric arc furnace, an appropriate amount of iron in the form of scrap iron, pig iron, or other cheap form of iron, andl then add to the molten iron commercial ferro-chromium of relatively high chromium percentage in sufficient amount to produce the desired chromium content inthe resulting alloy. For this purpose, ferrochromium containing 60% chromium may be satisfactorily used. The ferro-chromium may, moreover, be of a low grade contain- I' ing as high as 8% of carbon without objectionably increasing the carbon content of the resulting iron-chromium alloy. When forming theiron-*chromium alloy in an electric arc furnace, I ind it desirable to maintain a covering of green oxide of ychromium (Cr2'03) on the charge in the crucible, in order to avoid or counteract excessive absorption of carbon. by the` ironrchromium iron-chromium alloy maybe made direct from chromite by reductiony in an electric furnace with coke: 'orfanthracite coal. If

the resulting alloy" of iron and chromium l 1s too lowwin iron, scrap iron may be added to bring the iron content up to the desired percentage. 1 y

Ordinary iron is a good'heat conductor, but it will not stand up under the corrodng action of the combustion gases and sulfur fumes encounteredin ore roasting. lOn'the contrary, I have found that an alloy of iron and chromium, of the composition contemplated by the present invention, resists remarkably Well the actionof combustion gases and sulfur fumes. I practice, I have found when roasting sulfide ores, such as blend,

and chalcopyrites, that the sulfur fumes do.

not corrode the iron-chromium hearth of the furnace to an objectionable extent.

In an ore roasting furnace having itsk hearth or bed made of an alloy of iron and chromium, there is a pronounced economy in heat (compared vwith a similar furnace having a hearth of refractory material such as magnesite) since the heat ofthe combustion gases is rapidly transmitted by and through the metallic hearth. Again, an ironchromium hearth vpresents a hard, smooth,

Wear-resisting surface which permits the passage of the rakes through the ore charge at constant depth. The life of an ironchromium hearthis practically indefinite as compared with iron or refractory hearths. Moreover, with an iron-chromium hearth, there is no deterioration during suspension of the roasting operation, whereas a refractory hearth, under like circumstances, would crack-badly. A smaller space is also required in the case of hearths, beds, etc.` of iron-chromium, as compared with similar parts When made of refractory material such as magnesite. A furnace hearth made of the iron chromium alloy has the further advantage that it does not react or combine with either the metal or gangue constituents of the ore Which is undergoing roasting. y

An alloy of iron and chromium of the composition contemplated by the present invention, has a comparatively low coeliicient of heat expansion, about one-half that of copper. This means that on heating or cool-` ing a hearth made of an. alloy of iron and chromium, `no special allowance need be made for expansion andfcontraction.` By the practice of the invention, using a hearth of an iron-chromium` alloy distortion or fracture of hearths andarches, asfvvell as heat losses, due to poorvhearthand rarch 'p construction, are lin a verylarge measurev eliminated. y

Perhaps 4the most important advantage resultlng from the practice of the present invention in ore roasting apparatus resides in the greatly improved heat economy and eiiiciency. Thus, the iron-chromium hearth serves by its good heat conductivity to distribute by conduction heat from the hotter to the cooler portions of the furnace or ore roasting chamber.

While I have hereinbefore particularlyv discussed the a-dvantages arising from the use of iron-chromium hearths in ore roasting apparatus, it is to be understood that the invention contemplates the construction of other Walls of the apparatus of an alloy of iron and chromium. Thus, in its broader aspect, the invention involves constructing such Walls of the ore-roasting apparatus as Y are exposed to the roasting temperatures and Which at the same time contribute by conduction to the distribution of heat through the furnace of the iron-chromium alloy. Thus substantially the entire furnace (With the exception of the outer shell and the insulating brick lining of the same) may advantageously be made of an alloy composed chiey of iron and chromium of the 4composition hereinbefore disclosed.

I claim l. An apparatus for roasting ores having l such walls thereof as are exposed to the roasting temperatures and which contribute by conduction to the distribution of heat through the furnace made of an alloy of iron and chromium containing not less than and not more than 60% of chromium.

2. An apparatus for roasting ores having such Walls thereof as are exposed to the roasting temperatures and which contribute by conduction to the distribution of heat through the furnace made of an alloy of iron and chromium containing about 33% to 36% of chromium.

3. An ore roasting furnace having a hearth made of an alloy of iron and chromium containing not less than 30% and not more than 60% of chromium.

4. An ore roasting furnace having a hearth made of an alloy of iron and chromium containing about 33% to 36% of chromium.v

In testimony whereof I affix my, signature.

COLIN G. FINK. 

